Isolation structure of fin field effect transistor

Abstract

A representative fin field effect transistor (FinFET) includes a substrate having a major surface; a fin structure protruding from the major surface having a lower portion comprising a first semiconductor material having a first lattice constant; an upper portion comprising the first semiconductor material. A bottom portion of the upper portion comprises a dopant with a first peak concentration. A middle portion is disposed between the lower portion and upper portion, where the middle portion comprises a second semiconductor material having a second lattice constant different from the first lattice constant. An isolation structure surrounds the fin structure, where a portion of the isolation structure adjacent to the bottom portion of the upper portion comprises the dopant with a second peak concentration equal to or greater than the first peak concentration.

What is claimed is: 
     
       1. A method comprising:
 forming a first recess and a second recess in a substrate, a portion of the substrate between the first recess and the second recess forming a fin; 
 filling the first recess and the second recess with a dielectric material; 
 doping the dielectric material with a dopant, the dielectric material comprising a first peak concentration of the dopant; 
 removing a portion of the fin to form a fin recess; 
 partially filling the fin recess with a first semiconductor material; 
 filling a remaining portion of the fin recess with a second semiconductor material, the second semiconductor material being different from the first semiconductor material; and 
 doping the second semiconductor material with the dopant, the second semiconductor material comprising a second peak concentration of the dopant, the second peak concentration of the dopant being equal to or less than the first peak concentration of the dopant. 
 
     
     
       2. The method of  claim 1 , wherein the substrate comprises the second semiconductor material. 
     
     
       3. The method of  claim 1 , wherein doping the dielectric material with the dopant comprises performing an implantation process at an energy between about 50 KeV and about 100 Kev and at a dose between about 1E13 atoms/cm 2  to about 1E14 atoms/cm 2 . 
     
     
       4. The method of  claim 1 , wherein doping the second semiconductor material with the dopant comprises performing an implantation process at an energy between about 50 KeV and about 100 Kev and at a dose between about 1E13 atoms/cm 2  to about 1E14 atoms/cm 2 . 
     
     
       5. The method of  claim 1 , wherein a ratio of the first peak concentration of the dopant to the second peak concentration of the dopant is between about 2 to about 4. 
     
     
       6. The method of  claim 1 , wherein doping the second semiconductor material with the dopant further comprises doping the dielectric material with the dopant, the dielectric material comprising a third peak concentration of the dopant. 
     
     
       7. The method of  claim 1 , further comprising performing an oxidation process to form a pair of notches extending into opposite sides of the first semiconductor material. 
     
     
       8. A method comprising:
 patterning a substrate to form a first recess and a second recess in the substrate, a portion of the substrate between the first recess and the second recess forming a fin; 
 depositing a dielectric material in the first recess and the second recess; 
 implanting a dopant into the dielectric material, the dielectric material having a first peak concentration of the dopant at a first height above a bottom of the first recess; 
 etching the fin to form a fin recess; 
 selectively growing a first semiconductor material in the fin recess, a topmost surface of the first semiconductor material being below a topmost surface of the dielectric material; 
 selectively growing a second semiconductor material overt the first semiconductor material in the fin recess; and 
 implanting the dopant into the second semiconductor material, the second semiconductor material having a second peak concentration of the dopant at a second height above the bottom of the first recess, the second peak concentration of the dopant being equal to or less than the first peak concentration of the dopant, the first height being different from the second height. 
 
     
     
       9. The method of  claim 8 , wherein the first height is greater than the second height. 
     
     
       10. The method of  claim 9 , wherein a ratio of the first height to the second height is between about 1 and about 1.5. 
     
     
       11. The method of  claim 9 , wherein implanting the dopant into the dielectric material comprises performing an implantation process at an energy of about 60 KeV. 
     
     
       12. The method of  claim 8 , wherein the first height is less than the second height. 
     
     
       13. The method of  claim 12 , wherein a ratio of the first height to the second height is between about 0.5 and about 0.9. 
     
     
       14. The method of  claim 12 , wherein implanting the dopant into the dielectric material comprises performing an implantation process at an energy of about 120 KeV. 
     
     
       15. A method comprising:
 etching a substrate to form a first trench and a second trench in the substrate, a portion of the substrate between the first trench and the second trench forming a fin; 
 depositing a dielectric material in the first trench and the second trench; 
 performing a first implantation process on the dielectric material, the dielectric material comprising a first peak concentration of a dopant at a first height above a bottom of the first trench; 
 etching the fin to form a fin recess, a remaining portion of the fin having a second height above the bottom of the first trench, the second height being less than the first height; 
 forming a first semiconductor material in the fin recess, a topmost surface of the first semiconductor material being below a topmost surface of the dielectric material; 
 forming a second semiconductor material over the first semiconductor material in the fin recess, a topmost surface of the second semiconductor material being level with the topmost surface of the dielectric material; and 
 performing a second implantation process on the second semiconductor material, the second semiconductor material comprising a second peak concentration of the dopant at a third height above the bottom of the first trench, the second peak concentration of the dopant being equal to or less than the first peak concentration of the dopant, the first height being different from the third height. 
 
     
     
       16. The method of  claim 15 , wherein the first height is greater than the third height. 
     
     
       17. The method of  claim 15 , further comprising performing a third implantation process on the dielectric material, the dielectric material comprising a third peak concentration of the dopant at a fourth height above the bottom of the first trench, the second peak concentration of the dopant being equal to or less than the third peak concentration of the dopant, the fourth height being different from the third height, the third implantation process being performed after the first implantation process and before the second implantation process. 
     
     
       18. The method of  claim 17 , wherein the first implantation process is performed at a greater energy than the third implantation process. 
     
     
       19. The method of  claim 17 , wherein the fourth height is less than the third height. 
     
     
       20. The method of  claim 15 , further comprising performing a third implantation process on the dielectric material, the third implantation process being performed concurrent with the second implantation process.